1. Field of the Invention
The present invention is directed to a system for detecting incipient arc flash conditions.
2. Description of the Related Art
Arc flash is an extremely dangerous, and sometimes lethal, condition arising in electrical equipment wherein an electrical current short circuits across all air gap between conductors. Arcing can occur because of insulation failure, contacting a test probe to the wrong surface, or because of an accidental slip of a tool, etc. Low voltage (e.g. less than 240 volts) and low amperage (e.g., less than 1,000 amps) circuits present negligible risk of arc flash. However, with electrical circuits operating, for example, at several hundred volts and several thousand amps, the energy radiated by an arc flash can be several megawatts. In an arc flash the air becomes ionized, ad metal components are vaporized and blasted outward. Vaporized metal expands to 67,000 times the volume of solid metal and maintains the arc until the circuit is opened. The energy of the arc can create a plasma fireball at a temperature of 20,000° C., four times the temperature of the surface of the sun, which explodes outward, carrying with it bits of molten metal, loose pieces of equipment, and other debris. Personnel within the blast radius can be blown off their feet, suffer broken bones, and punctured organs. The arc flash can ignite clothing and cause burns almost instantaneously which may take months to heal. The intense ultraviolet radiation (U) from the flash can cause damage to the eye. A single arc flash incident can cause millions of dollars of damage to personnel and equipment within a fraction of a second, in addition to the pain and suffering of personnel injured by the flash, as well as their families.
One of the ways to mitigate the risk of damage and injury is by the use of protective clothing, by restricting work on energized equipment, and procedures mandated by regulatory agencies.
However, use of protective gear which fully encloses the personnel makes it difficult to perform maintenance operations. Moreover, maintenance may need to be performed on energized equipment.
An arc flash is terminated by opening the electric circuit to cut off the energy supply. The longer it takes to open the circuit the more energy and damage is propagated by the arc flash. What is needed is a system and method for detecting incipient arc flash conditions and responding thereto in sufficient time to de-energize the circuit before major damage has occurred. By “incipient arc flash” is meant that the arc flash has not progressed to the level of causing extensive damage. Typically, an arc flash is considered incipient if it has not progressed for more than a few milliseconds.